GHK Cu is a naturally occurring tripeptide in human plasma. Levels average 200 ng ml at age 20 and drop to 80 ng ml by age 60 (Pickart et al., 2020). That decline tracks with PDF) The Human Tripeptide GHK Cu in Prevention of Oxidative Stress and Degenerative Conditions of Aging: Implications for Cognitive Health The glycyl l histidyl l lysine Cu2+ tripeptide complex attenuates lung inflammation and fibrosis in silicosis by targeting peroxiredoxin 6 ScienceDirect Frontiers Exploring the beneficial effects of GHK Cu on an experimental model of colitis and the underlying mechanisms GHK Cu vs AHK Cu: Which Copper Peptide Is More Effective?